HFC (hydrofluorocarbon) systems, which have zero ozone depletion potential, are used increasingly as the operating refrigerants for conventional refrigeration apparatuses, but on the other hand, the HFC-based refrigerants, which have very high global warming potentials, are causing problems recently. Thus, under study are refrigeration apparatuses that use a refrigerant mainly containing a chlorine atom-free low-global warming potential hydrofluoroolefin having a carbon-carbon double bond. Various studies are made on the sliding materials used in these kinds of compressors employing the conventional HFC-based refrigerants, such as vanes and pistons in rotary compressors, for assure reliability (see, for example, Patent Document 1).
FIG. 5 is a horizontal cross-sectional view illustrating the rotary compressor used with a conventional HFC (hydrofluorocarbon)-based refrigerant described in Patent Document 1. In the configuration, a piston 33, which is inserted along the internal surface of a cylinder 31, rotates by rotation of the shaft 32, suctioning and compressing a refrigerant gas respectively in a suction chamber and a compression chamber partitioned by a vane 34. The region of the rotary compressor severely damaged by abrasion in the mechanical configuration above is the area where the tip of the vane 34 and the peripheral surface of the piston 33 are in contact with each other, and it is a boundary lubrication region where the tip of the vane 34 is pressed onto the peripheral surface of the piston 33 by large force from the back face of the vane 34 because of the pressure difference between discharge and suction pressures.
For that reason, the vane is subjected to nitridation treatment or the surface thereof to CrN or TiN ion plating, for improvement in abrasion resistance to assure reliability.